Airborne anomalies (4)
I believe the answer is:
ufos
'airborne anomalies' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ufos that I've seen before include "Mysterious phenomena" , "Initially and formally, flying saucers" , "Supposed alien craft" , "Unauthorised traffic from outer space?" , "Mysterious things" .)